TCP/IP基础

UDP提供无连接服务
UDP的数据格式:

#ifdef __FAVOR_BSD
struct udphdr {
         u_int16_t uh_sport;           /* source port */
         u_int16_t uh_dport;           /* destination port */
         u_int16_t uh_ulen;            /* udp length */
         u_int16_t uh_sum;             /* udp checksum */
};
#else

struct udphdr {
  u_int16_t     source;
  u_int16_t     dest;
  u_int16_t     len;
  u_int16_t     check;
};
#endif

TCP是面向连接的,切实全双工的。
TCP协议数据段:
这里写图片描述

struct tcphdr {
    WORD    SourPort;
    WORD    DestPort;
    DWORD   SeqNo;
    DWORD   AckNo;
    BYTE        HLen;
    BYTE        Flag;
    WORD    Window;
    WORD    ChkSum;
    WORD    UrgPtr;
    /* Put options here. */
}; 

TCP的time_wait:
执行主动关闭的那端进入这种状态。这个端点在该状态的持续时间是2MSL(最长分节生命周期)。
网络中的几类地址:
物理地址:即MAC地址 (数据链路层)
逻辑地址:即IP地址
端口地址:应用程序端口号
域名地址:取代IP地址记忆

IPv4的套接字地址:

/* Internet address.  */
typedef uint32_t in_addr_t;
struct in_addr
  {
    in_addr_t s_addr;
  };
/* Structure describing an Internet socket address.  */
struct sockaddr_in
  {
    __SOCKADDR_COMMON (sin_);
    in_port_t sin_port;         /* Port number.  */
    struct in_addr sin_addr;        /* Internet address.  */

    /* Pad to size of `struct sockaddr'.  */
    unsigned char sin_zero[sizeof (struct sockaddr) -
               __SOCKADDR_COMMON_SIZE -
               sizeof (in_port_t) -
               sizeof (struct in_addr)];
  };

IPv6套接字地址:

struct in6_addr
  {
    union
      {
    uint8_t __u6_addr8[16];
#ifdef __USE_MISC
    uint16_t __u6_addr16[8];
    uint32_t __u6_addr32[4];
#endif
      } __in6_u;
#define s6_addr         __in6_u.__u6_addr8
#ifdef __USE_MISC
# define s6_addr16      __in6_u.__u6_addr16
# define s6_addr32      __in6_u.__u6_addr32
#endif
  };

/* Ditto, for IPv6.  */
struct sockaddr_in6
  {
    __SOCKADDR_COMMON (sin6_);
    in_port_t sin6_port;    /* Transport layer port # */
    uint32_t sin6_flowinfo; /* IPv6 flow information */
    struct in6_addr sin6_addr;  /* IPv6 address */
    uint32_t sin6_scope_id; /* IPv6 scope-id */
  };

TCP套接字编程

tcp套接字网络编程的主要实现过程:
这里写图片描述
关于socket函数:

#include<sys/socket.h>
int socket(int family,int type,int protocol)

family指明了协议族。例如:AF_INET(IPv4协议);AF_INET6(IPV6协议);AF_ROUTE(路由套接口)
type指明了套接字类型。例如:
SOCK_STREAM字节流套接口(TCP);
SOCK_DGRAM数据包套接口(UDP);
SOCK_RAW原始套接口

protocol指明协议标志

端口与套接字

端口:访问网络不同计算机程序的编号
IP地址标记了不同的电脑,而域名则是iP地址便于记忆的别名

edemon@ubuntu:~$ ping www.baidu.com
PING www.a.shifen.com (119.75.218.70) 56(84) bytes of data.
这里写图片描述
socket的本义是插座。描述计算机之间不同程序之间的通信方式。TCP和UDP会遇到同时为多个应用程序同时并发进行通信的问题,为了区分不同的应用进程的应用和连接,需要使用应用程序与TCP/IP协议交互的套接字接口。
套接字:传输层协议+端口号+IP地址

域名和IP的相互转换

IP地址和网络地址:
网络地址很大一部分是由地址掩码决定的。
IP 转 domain:

#include <stdio.h>
#include <sys/socket.h>
#include <netdb.h> 
#include <netinet/in.h>
#include <arpa/inet.h>  
#include <errno.h> 
#include <string.h>

int  main()
{
   struct hostent *host;
   char addr[]="208.108.249.216"; //202.108.249.216  61.135.169.121   http://61.135.169.125/
   struct in_addr in;
   struct sockaddr_in addr_in; 

   host=gethostbyaddr(addr,sizeof(addr),AF_INET);
   if(host!=(struct hostent *)NULL)
   {
       memcpy(&addr_in.sin_addr.s_addr,host->h_addr,4);
       in.s_addr=addr_in.sin_addr.s_addr;
       printf("Domain name: %s \n",host->h_name);
       printf("IP length:    %d\n",host->h_length);
       printf("Type:    %d\n",host->h_addrtype);
       printf("IP          : %s \n",inet_ntoa(in));
    }
    else
    {  
        char *buffer = strerror(errno); 
          printf("%s\n",buffer);
    } 
}
/*
Domain name: 50-48-56-46.dr05.nrwc.ny.frontiernet.net 
IP length:    16
Type:    2
IP          : 50.48.56.46 
*/

domain 转IP:

#include <stdio.h>
#include <sys/socket.h>
#include <netdb.h>
#include <string.h>
#include <netinet/in.h>
#include <arpa/inet.h>

int  main()
{
   struct hostent *host;
   char hostname[]="www.baidu.com";
   char hostname2[]="www.012www.com";
   struct in_addr in;
   struct sockaddr_in sock_in;
   extern int h_errno;

   if((host=gethostbyname(hostname))!=NULL){
       //printf("%s\n",host->h_addr);
       memcpy(&sock_in.sin_addr.s_addr, host->h_addr, 4);
       in.s_addr=sock_in.sin_addr.s_addr;
       printf("Domain name: %s \n",hostname);
       printf("IP length:    %d\n",host->h_length);
       printf("Type:    %d\n",host->h_addrtype);
       /*inet_ntoa()用来将参数in所指的网络二进制的数字转换成网络地址,
       然后将指向此网络地址字符串的指针返回。*/
       printf("IP          : %s \n",inet_ntoa(in));
    }
    else{
        printf("Domain name: %s \n",hostname);
        printf("error: %d\n",h_errno);
        printf("%s\n",hstrerror(h_errno));
    }

   if((host=gethostbyname(hostname2))!=NULL){
       memcpy(&sock_in.sin_addr.s_addr,host->h_addr,4);
       in.s_addr=sock_in.sin_addr.s_addr;
       printf("Domain name: %s \n",hostname2);
       printf("IP          : %s \n",inet_ntoa(in));
       printf("IP length:    %d\n",host->h_length);
       printf("Type:    %d\n",host->h_addrtype);
    }
    else{
        printf("Domain name: %s \n",hostname2);
        printf("error: %d\n",h_errno);
            printf("%s\n",hstrerror(h_errno));
    }
}
/*
Domain name: www.baidu.com 
IP length:    4
Type:    2
IP          : 61.135.169.121 
Domain name: www.012www.com 
error: 1
Unknown host
*/

网络地址转换

对于不同的socket domain定义了一个通用的数据结构——套接字结构:

struct sockaddr
{
unsigned short int sa_family;
char sa_data[14];
};

sa_family 为调用socket()时的domain参数,即AF_xxxx值。
sa_data 最多使用14个字符长度。
此sockaddr结构会因使用不同的socket domain而有不同结构定义,例如使用AF_INET domain,其
socketaddr结构定义便为

struct socketaddr_in
{
unsigned short int sin_family;
uint16_t sin_port;
struct in_addr sin_addr;
unsigned char sin_zero[8];
};
struct in_addr
{
uint32_t s_addr;
};

sin_family 即为sa_family
sin_port 为使用的port编号
sin_addr.s_addr 为IP 地址
sin_zero 未使用。

struct hostent{
char * h_name;
char ** h_aliases;
short h_addrtype;
short h_length;
char ** h_addr_list;
};

主机字节序和网络字节序的转换:

unsigned long int htonl(unsigned long int hostlong);
将32位主机字符顺序转换成网络字符顺序
unsigned short int htons(unsigned short int hostshort);
将16位主机字符顺序转换成网络字符顺序
unsigned long int ntohl(unsigned long int netlong);
将32位网络字符顺序转换成主机字符顺序
unsigned short int ntohs(unsigned short int netshort);
将16位网络字符顺序转换成主机字符顺序

#include <stdio.h>
#include <arpa/inet.h>

int  main()
{
   long local;
   int port;
   local =123456;
   port=123456;
   printf("host 32 %ld -> net 32: %d\n",local,htonl(local));
   printf("host 16 %d -> net 16: %d\n",port,htons(port));
   printf("net 32 %d -> host 32: %d\n",htonl(local),ntohl(htonl(local)));
   printf("net 16 %d -> host 16: %d\n",htons(port),ntohs(htons(port)));  
   return 0;
}
/*
host 32 123456 -> net 32: 1088553216
host 16 123456 -> net 16: 16610
net 32 1088553216 -> host 32: 123456
net 16 16610 -> host 16: 57920
*/

long inet_addr(char *str)
将网络IP地址转化成10进制长整型数
头文件:

#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>

char *inet_ntoa(struct in_addr in);
将整数型地址转化成点分十进制地址(在计算机中经常使用长整型数表示IP地址)
表头文件

#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>

例子:

#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
int  main()
{
   struct in_addr ip;
   ip.s_addr=16885952;
   char *str=inet_ntoa(ip);
   printf("%s\n",str);
   printf("%u\n", inet_addr(str));
}
/*
192.168.1.1
16885952
*/

系统支持的网络服务

cat /etc/protocols
……
daytime     13/tcp
daytime     13/udp
netstat     15/tcp   
qotd        17/tcp      quote
msp     18/tcp              # message send protocol
msp     18/udp
chargen     19/tcp      ttytst source
chargen     19/udp      ttytst source
ftp-data    20/tcp
ftp     21/tcp
……

获取服务信息:

#include <stdio.h>
#include <netdb.h>   

int  main()
{
    struct servent *ser;
    if( ser=getservbyname("http","tcp"))  //通过名字获取网络服务
    {
       printf("name : %s\n",ser->s_name);
       printf("net port: %d  ", ser->s_port);
       printf("host port : %d\n",ntohs(ser->s_port));  //16位网络字符顺序转换成主机字符顺序
       printf("protocol:%s\n",ser->s_proto);
       printf("alias: %s\n",ser->s_aliases[0]);
    }
    else
    {
        printf("there is no such a service.\n");
    }
    puts("---------------------------------------------");
    if( ser=getservbyname("hehe","tcp"))
    {
       printf("name : %s\n",ser->s_name);
       printf("net port: %d  ", ser->s_port);
       printf("host port : %d\n",ntohs(ser->s_port));
       printf("protocol:%s\n",ser->s_proto);
       printf("alias: %s\n",ser->s_aliases[0]);
    }
    else
    {
        printf("there is no such a service.\n");
    }   
    puts("---------------------------------------------");  //通过端口号获取网络服务
    if( ser=getservbyport(htons(21),"tcp"))  //将16位主机字符顺序转换成网络字符顺序
    {
       printf("name : %s\n",ser->s_name);
       printf("net port: %d  ", ser->s_port);
       printf("host port : %d\n",ntohs(ser->s_port));  
       printf("protocol:%s\n",ser->s_proto);
       printf("alias: %s\n",ser->s_aliases[0]);
    }
    else
    {
        printf("there is no such a service.\n");
    }
}
/*
name : http
net port: 20480  host port : 80
protocol:tcp
alias: www
---------------------------------------------
there is no such a service.
---------------------------------------------
name : ftp
net port: 5376  host port : 21
protocol:tcp
alias: (null)
*/

捕获错误

void herror(const char *s);
可以显示网络函数上出现的错误。先输出这个字符串,然后输出错误信息。
extern int h_errno
可以捕获错误编号。
char *hstrerror(int err)
返回错误编码对应的错误信息。
三个和错误相关的函数或变量都与头文件netdb.h相关

#include <stdio.h>
#include <netdb.h>
int  main()
{
    herror("result : ");
    extern int h_errno;
    printf("%s\n", hstrerror(h_errno));
}

获取协议数据

系统支持的协议:

ip  0   IP      # internet protocol, pseudo protocol number
hopopt  0   HOPOPT      # IPv6 Hop-by-Hop Option [RFC1883]
icmp    1   ICMP        # internet control message protocol
igmp    2   IGMP        # Internet Group Management
ggp 3   GGP     # gateway-gateway protocol
ipencap 4   IP-ENCAP    # IP encapsulated in IP (officially ``IP'')
st  5   ST      # ST datagram mode
tcp 6   TCP     # transmission control protocol
egp 8   EGP     # exterior gateway protocol
igp 9   IGP     # any private interior gateway (Cisco)
pup 12  PUP     # PARC universal packet protocol
udp 17  UDP     # user datagram protocol
hmp 20  HMP     # host monitoring protocol
xns-idp 22  XNS-IDP     # Xerox NS IDP
rdp 27  RDP     # "reliable datagram" protocol
iso-tp4 29  ISO-TP4     # ISO Transport Protocol class 4 [RFC905]
dccp    33  DCCP        # Datagram Congestion Control Prot. [RFC4340]
xtp 36  XTP     # Xpress Transfer Protocol
ddp 37  DDP     # Datagram Delivery Protocol
idpr-cmtp 38    IDPR-CMTP   # IDPR Control Message Transport
ipv6    41  IPv6        # Internet Protocol, version 6
ipv6-route 43   IPv6-Route  # Routing Header for IPv6
ipv6-frag 44    IPv6-Frag   # Fragment Header for IPv6
idrp    45  IDRP        # Inter-Domain Routing Protocol
rsvp    46  RSVP        # Reservation Protocol
gre 47  GRE     # General Routing Encapsulation
esp 50  IPSEC-ESP   # Encap Security Payload [RFC2406]
ah  51  IPSEC-AH    # Authentication Header [RFC2402]
skip    57  SKIP        # SKIP
ipv6-icmp 58    IPv6-ICMP   # ICMP for IPv6
ipv6-nonxt 59   IPv6-NoNxt  # No Next Header for IPv6
ipv6-opts 60    IPv6-Opts   # Destination Options for IPv6
rspf    73  RSPF CPHB   # Radio Shortest Path First (officially CPHB)
vmtp    81  VMTP        # Versatile Message Transport
eigrp   88  EIGRP       # Enhanced Interior Routing Protocol (Cisco)
ospf    89  OSPFIGP     # Open Shortest Path First IGP
ax.25   93  AX.25       # AX.25 frames
ipip    94  IPIP        # IP-within-IP Encapsulation Protocol
etherip 97  ETHERIP     # Ethernet-within-IP Encapsulation [RFC3378]
encap   98  ENCAP       # Yet Another IP encapsulation [RFC1241]
#   99          # any private encryption scheme
pim 103 PIM     # Protocol Independent Multicast
ipcomp  108 IPCOMP      # IP Payload Compression Protocol
vrrp    112 VRRP        # Virtual Router Redundancy Protocol [RFC5798]
l2tp    115 L2TP        # Layer Two Tunneling Protocol [RFC2661]
isis    124 ISIS        # IS-IS over IPv4
sctp    132 SCTP        # Stream Control Transmission Protocol
fc  133 FC      # Fibre Channel
mobility-header 135 Mobility-Header # Mobility Support for IPv6 [RFC3775]
udplite 136 UDPLite     # UDP-Lite [RFC3828]
mpls-in-ip 137  MPLS-in-IP  # MPLS-in-IP [RFC4023]
manet   138         # MANET Protocols [RFC5498]
hip 139 HIP     # Host Identity Protocol
shim6   140 Shim6       # Shim6 Protocol [RFC5533]
wesp    141 WESP        # Wrapped Encapsulating Security Payload
rohc    142 ROHC        # Robust Header Compression

获取协议信息的例子:

#include <stdio.h>
#include <netdb.h>   

int  main()
{
    struct protoent *pro;
    pro=getprotobyname("tcp");  // by protocol name 
    printf("protocol name : %s\n",pro->p_name);  
    printf("protocol number : %d\n",pro->p_proto);
    printf("protocol alias: %s\n",pro->p_aliases[0]);
    puts("------------------------------");
    pro=getprotobynumber(2);   // by protocol number 
    printf("protocol name : %s\n",pro->p_name);  
    printf("protocol number : %d\n",pro->p_proto);
    printf("protocol alias: %s\n",pro->p_aliases[0]);
}

protocol name : tcp
protocol number : 6
protocol alias: TCP
------------------------------
protocol name : igmp
protocol number : 2
protocol alias: IGMP

其他的套接字函数

自己的主机IP地址:
ifconfig
下面是ANSI C 中的字节操作函数:
1.
void *memset(void *s, int c, size_t n);
memset()会将参数s所指的内存区域前n个字节以参数c填入,然后返回指向s的指针。
2.
void *memcpy(void *dest, const void *src, size_t n);
memcpy()用来拷贝src所指的内存内容前n个字节到dest所指的内存地址上。与strcpy()不同的是,
memcpy()会完整的复制n个字节,不会因为遇到字符串结束’\0’而结束。
3.
int memcmp(const void *s1, const void *s2, size_t n);
memcmp()用来比较s1和s2所指的内存区间前n个字符。

字符串IP和二进制IP的相互转换(仅能处理IPv4):
int inet_aton(const char *cp, struct in_addr *inp);
函数说明
inet_aton()用来将参数cp所指的网络地址字符串转换成网络使用的二进制的数字,然后存于参数inp所
指的in_addr结构中。

返回值
成功则返回非0值,失败则返回0。

#include <stdio.h>
#include<sys/socket.h>
#include<netinet/in.h>
#include<arpa/inet.h>

int main(){
    struct in_addr numstr;
    char IP[20]="192.160.8.60";
    if(inet_aton(IP,&numstr)){
         printf("0x%x\n",numstr.s_addr);
    }    
    return 0;
}
/*
0x3c08a0c0
*/

inet_pton
int inet_pton(int af, const char *src, void *dst);
用于点分十进制转成二进制整数(16进制)。
成功返回1,af无效返回0,出错返回-1,指针dst存储得到的IP地址。

inet_ntop
const char *inet_ntop(int af, const void *src, char *dst, socklen_t cnt);
二进制整数(16进制)转换成点分十进制。
两者可以同时处理IPv4, IPv6.
AF_INET 是一个IPv4 网络协议的套接字类型

#include <stdio.h>
#include <arpa/inet.h>
int main ()
{
    char IPstr1[20]="192.18.0.9"; 
    char IPstr2[20];
    struct in_addr s; // IPv4地址结构体

    printf("%d\n",AF_INET);
    inet_pton(AF_INET, IPstr1, (void *)&s);
    printf("inet_pton: 0x%x\n", s.s_addr); //二进制整数(16进制)字节序

    inet_ntop(AF_INET, (void *)&s, IPstr2, sizeof(IPstr2));
    printf("inet_ntop: %s\n", IPstr2); //点分十进制

    return 0;
}
/*
2
inet_pton: 0x90012c0
inet_ntop: 192.18.0.9
*/

从进程到内核传递套接字地址结构的函数常有3个——bind, connect, sendto
从内核到进程传递套接字地址结构的函数常有四个accept, recvfrom, getsockname, getpeername
bind()对socket定位

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